What's new in Linux 2.6.35

by Thorsten Leemhuis

Measures to support the power saving mechanisms of AMD graphics chips, network code optimisations for multi-core processors, features for de-fragmenting the working memory and an improved support of the power management and turbo features offered by modern processors are among the highlights of the new kernel version.

After a development time of almost two-and-a-half months, Linus Torvalds has released version 2.6.35 of the Linux kernel. Like other versions in the main development branch of Linux, the new kernel offers numerous further improvements over its predecessor, Linux 2.6.34, which was released in mid-May.

For instance, the kernel now supports many power management features offered by Radeon graphics chips and supports the Intel-Ironlake driver's H.264 decoding feature. The Btrfs file system can handle direct I/O and apparently no longer glitches when the storage space approaches full capacity. Various improvements introduced by Google promise a higher network throughput and less latency on multi-core systems.

Other additions include code optimisation measures for the power management functions offered by modern processors and full support of the Turbo Core feature of AMD's recent six-core CPUs. Also new are the tracing interfaces for the KVM hypervisor, a further kernel configuration program and features for de-fragmenting the working memory. Plus there are the usual hundreds of new or improved drivers – offering such advancements as extended USB 3.0 support and improved transmission rates for the ath_5k Wi-Fi driver.

The following Kernel Log offers an overview of these and many further new features of Linux 2.6.35. These changes will eventually impact all Linux users because the adoption of Linux 2.6.35 or its successors by future Linux distributions will ensure the widespread use of new kernels; at the end of this article, the Kernel Log will also take a peek at the advancements some developers have already prepared for Linux 2.6.36.

Graphics drivers

The rudimentary support of the power management functions of Radeon graphics chips already introduced in Linux 2.6.34 has been extended and optimised considerably in 2.6.35. How aggressive the driver's power saving efforts will be can be determined via /sys/class/drm/card0/device/power_method. For instance, writing "dynpm" to this file activates the fully automatic dynamic power management. Alternatively, by writing "profile" to the file, users can enable one of four profiles in the file /sys/class/drm/card0/device/power_profile: "default" enables the standard GPU and memory clocks, "low" activates a power-saving mode, "high" a performance mode, and "auto" automatically switches between "low" and "high" depending on the power supply.

The driver for the graphics cores found in many Intel motherboard and notebook chip-sets now includes all the basics (such as the bit stream decoder ring buffer) required for using the H.264 decoding functions offered by Ironlake CPUs, which have a graphics core. New userland software such as the libva as well as player software which supports this library is also required to use these functions; further details and download links can be found on a web page maintained by Intel. Among the other additions for the driver is support of memory self-refresh with Ironlake processors – according to tests by the developer, the latter reduced a test netbook's power consumption by one Watt.